Circuit breaker



vDee. 18, 1951 L E FISHER 2,579,252

CIRCUIT BREAKER Filed Feb. 5, 1945 2 SHEETS-SHEET l Dec. 18, 1951 E.FISHER 2,579,252

CIRCUIT BREAKER Filed Feb. 5. 1945 2 SHEETS-SHEET 2 mzlllnlzq.

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ww @M Patented Dec. 18, 1951 CIRCUIT BREAKE Lawrence E. Fisher, Detroit,Mich., assigner to BullDog Electric Products Company, Detroit, Mich., acorporation of West Virginia Application February 5, 1945, Serial No.578,171 3 claim.. (ci. zon-11s) This application relates to overloadrelease circuit breakers, generally, and `more specifically concerns animproved overload release mechanism that is particularly adaptable tothe type circuit breaker disclosed in U. S. Patent No. 2,385,727 issuedon September 25, 1945, to Elwood T. Platz.

In the type of circuit breaker described in the aforementioned patent,the release mechanism includes a releasable latch consisting of abimetal latching element having a portion thereof arranged inoverlapping relation with an abutment. On the occurrence of atemperature rise such as would be occasioned by an overload in thecircuit, the overlapping portion of the bimetal tends to work away fromthe abutment and, being spring loaded, frees itself from the abutment tothereby release a contactor. In such devices the latching element tendsto work away from the abutment on any temperature rise, regardless ofwhether that temperature rise is caused by ambient temperature, byheating due to prolonged moderate overload, or by a momentary excessiveoverload in the controlled circuit. As release characteristics aredependent. among other things, upon 25 the amount of overlap between thebimetal and the abutment, it is desirable to prevent the overlap fromchanging except on temperature rise occasioned by overload. Since theamount of overlap also affects thespeed of opening of the circuitbreaker and as it is desirable to have the circuit opened rapidly on theoccurrence of an excessive overload of large magnitude, it is also`desirable to have as small an amount of overlap as possible. v

In order to obtain faster opening than is possible in circuit breakershaving bimetal latching elements alone, an over-controlling magneticrelease has been supplied in circuit breakers which release is adjustedto cause faster release in the desired range of overload. See forexample, copending application Serial No. 724,430, filed on January 25,1947, in the names of William H. Frank, Elwood T. Platz, and Russell S.Davis, and assigned to the assignee of the present application. However,such combinations require more space and materials and are moreexpensive to produce than the type using only bimetallic elements.Moreover, the effects of ambient temperature on the bimetal elements ofthe known combinations, acts to alter the speed of release in the rangeof overloads when release is eifected by working of the bimetal elementsin the release direction.

Therefore, a primary feature of the present invention is the provisionof a novel latching arrangement for circuit breaker. that permits a widerange of choice of release characteristics. A further feature of thepresent invention is the provision of a bimetal latching arrangement fora circuit breaker that maintains a predetermined release characteristicirrespective of variations of the ambient temperature at the circuitbreaker. A further feature is in the provision of an improved bimetallatching arrangement for circuit breakers that provides a very quicktrip when the circuit breaker is closed on an existing overload. A stillfurther feature of the present invention resides in the provision of abimetal latching arrangement wherein two bimetals are provided and theyare arranged to provide slow release on moderate overloads and quickrelease on excessive overloads. These and other features of the presentinvention will become apparent from the description of the drawingswherein:

Fig. 1 is a fragmentary view of the circuit breaker in a closed positionand including a preferred embodiment of the present invention.

Fig. 2 is a view along the lines A-A of Fig. 1. Fig. 3 is a view alongthe lines of B-B of Fig. 1. Fig. 4 is a fragmentary view of the circuitbreaker of Fig. l in a'tripped, or opened circuit position.

Fig. 5 is aview along the lines C-C of Fig. 4. Fig. 6 is a view alongthe lines D-D of Fig. 4. Fig. 7 is a perspective of the circuit breakerof F18. 1.- Referring now to Fig. 1 of the drawings, the circuit breakermechanism is illustrated as being enclosed in a case Il, and as having aconstruction and mechanism. the major parts of which, are much similarto the mechanism of the aforementioned Patent No. 2,385,727. Thisconstruction and ymechanism includes the line terminal I4 secured to thecase I0, and arranged to support the stationary contact 44. A movablecontactor 50, carrying the contact 48, is pivoted by the rivet 5| topermit the contact 48 to make butt contact with the stationary contactIl. The movable contacter 50 has an L-shaped portion having a lug 58 forholding compression spring 5i, which in turn is seated in the springseat 30 of casing Il. The spring 56 not only acts to coerce the movablecontacter 50 in a counterclockwise direction, but also serves to coercethe lug I8 and the movable contacter 50 toward the insulation holdingplate il. Also as in the aforementioned patent, rigidly secured to themovable contact 5I. by means of the rivet Si, is a bimetallic lachlnlelement l2, which, in the mamada s latched position illustrated in Figs.1', 2, and .3, has a hook 60, formed of an edge thereof, abut tingagainst the abutment edge 5| formed of the insulation holding plate 53.As'the spring 56 tends to coerce the movable contacter 55 towards theinsulating holding plate 53, it also tends to force the bimetal 52towards the plate 53. In order that the bimetal 52 may be sensitive tothe amount ci current through the circuit breaker, the current istransmitted through it, by means of the exible loop 55, and thusly, whenan overload occurs. heating takes-place in the bimetallic strip 52 andit tends to warp away trom the plate 53. However, the spring 55 alsotends to force the hook 55 to the right, as viewed in Fig. 3. Hence theamount of overlap o the hook 55 on the abutment edge 5| of plate 53 isdetermined by the adjusting screw 25|, which is carried by member 200rigidly secured to moveable contact 50 by rivet 5|. The hook 50 o!bimetal 52 must warp the amount of the overlap in order to be treed ofthe abutment edge 5|. In other words, the current passing through thebimetal element 52, must be of a value (on overload) to heat the element52 to cause it to warp an amount suillcient tolmove the hook 50 (to thelett as viewed in Fig. 3) free of the abutment edge 6|, whereupon thespring 55 moves the movable contact and its lassociated elements 52 and205 to the tripped or open circuit position illustrated in Figs. 4, 5.and 6.

From the above description, it can be seen that the position of theadjusting screw 20| determines the distance that the hook 55 must travelaway from the plate 53, before the circuit breaker will trip to the opencircuit position. As the spring 5 5 coerces the bimetal 52 and the hook60 toward the plate 55, the screw 20|, in resting on the plate 53,limits the amount which the hook,

this construction, as the bimetallic strip 52 tends v to warp and alterits release characteristics through altering the amount of overlapbetween the hook and the abutment edge 5|, as the second bimetal element200 also tends to warp,

in response to ambient temperature, in the same temperature compensatingstrip 255 does not e have time to operate. Hence the strip E2 may beconsidered a quick or rapid actingbimetal, while the strip 200 a slowacting bimetal.

In addition to maintaining the proper release characteristicsnotwithstanding ambient temperature variations, a further advantage isderived from the construction set forth. It an attempt is made to close,or latch the breaker on an existing overload, the strip 52 will becaused to heat and warp. but this condition will not be transmitted tothe strip 200. as the time element is too short to permit heat transferand subsequent warping of bimetal strip 200. Thus, the strip 200 notonly derives one advantage from being positioned close to the bimetalstrip 52, whereby the ambient temperature of the strip 52 will beaccurately reected in the strip 200, but

also this proximity does not become a disadvantage. upon the occurrenceof an excessive overload.

Iclaim:

1. In an overload release circuit breaker, a xed contact, a movablecontact, a member carrying said movable contact and mounted to move thelatter into and out of engagement with said iixed contact, means urgingsaid member in a dlrection to separate said contacts, a bimetalliclatching element secured to said member, an abutment arranged normallyto block contactopening movement of said latching element and saidmember, said latching element being in circuit'with said contacts to beywarped free of said abutment upon passage of an overload current, meansurging said latching element in the direction of increased overlap withrespect to said abutment, and a bimetallic ambient-temperaturecompensating element arranged adjacent said latching element anddisposed to contact the same so as to maintain constant the amount ofoverlap between said latching element and said abutment irrespective ofchanges in ambient temperature.

2. The device in accordance with claim 1, in which a single springconstitutes the means for urging said member in contact-openingdirection and the means for urging said latching element in thedirection of increased overlap.

3. The device in accordance with claim 1, lin which said'compensatingelement is disposed in heat-receiving relation to said latching elementwhereby it will operate to slow down the unlatching movement of saidlatching element for moderate overloads without affecting the speed ofAunlatching movement for excessive overloads.

LAWRENCE E. FISHER.

REFERENCES CITED I .The following references are of record in the ille-of this patent:

s UNITED STATES PATENTS Number Getchell Dec.`7, 1948

